The present invention relates to a system for and a method of actively controlling torque distribution unit a pair of primary driving wheels and a pair of secondary driving wheels of a motor vehicle.
JP No. 61-178233 discloses a system for controlling torque distribution of a motor vehicle of the four-wheel drive type. This known system includes a limited slip differential between a pair of primary driving wheels and a transfer unit which is capable of changeover between a four-wheel drive and a two-wheel drive. When the two-drive is selected, a differential limiting force is not applied to the differential, allowing a slip between the main driving wheels, whereas when the four-wheel drive is selected, the differential limiting force is applied to the differential, limiting the slip between the driving wheels.
According to this known system, since there is no differential limiting force when the two-wheel drive is selected, the inner wheels tend to spin when the vehicle is subject to a high side acceleration (more than 0.8 G, for example) and a high longitudinal acceleration (more than 0.2 G, for example) during the vehicle making a turn with the two-wheel drive. This results in loss of driving force. When the vehicle make a turn with the four-wheel drive state and is subject to a mudium degree of side acceleration (more than 0.5 to 0.7 G, for example) and a medium degree of longitudinal acceleration (0.2 G, for example), the vehicle is subject to understeer owing to the application of the differential limiting force to the diffrential mechanism between the primary driving wheels. Thus, the readiness of the vehicle to change its heading (yawing moment) drops.
An object of the present invention is to provide a system for and a method of actively controlling torque distribution over primary and secondary driving wheels of a motor vehicle such that the torque distribution over all of the primary and secondary driving wheels is appropriately varied according to varying running modes of the vehicle.